Venetian blind trimmers are used to adapt a premanufactured blind to the specific requirements of an opening by trimming one end of each slat. For this purpose, cutting dies are attached to the jaws of a scissors-action hand tool similar to a tin snip. A depth gauge is connected to one of the dies to provide a uniform measurement for evenly modifying the length of each slat. The typical scissors-action venetian blind trimmer brings the dies together with a variable shear so that a slat is trimmed progressively from one edge to the other as the pivoted handles of the trimmer are closed. An ordinary shear cannot be used for this trimming operation because venetian blind slats have curved corners. These curved corners must be preserved for cosmetic uniformity among slats of a single blind.
The task of trimming venetian blind slats with acceptable uniformity presents several problems. First, the slats are slightly bowed from front to rear and tend to flatten under the pressure of a cutting tool, presenting an alignment problem between the slats and the cutting dies. Second, the slats are constructed from thin sheet material, such as aluminum, so the edges are subject to burring if the clearance between the dies is excessive. Burring is a recurrent problem with scissors-action trimmers, since alignment between the dies is controlled only at the single pivot point between the shear handles. If either burring or an uneven corner results from a trimming operation, it is necessary to retrim or to replace the slat. Retrimming one slat may produce an unevenness among the slats. Therefore, it is highly desirable for a trimmer to be accurate and consistent in its operation.
U.S. Pat. No. 4,272,888 to Hartmeister discloses a parallel action die cutting hand tool having a pair of scissors-action handle levers pivotally connected together on a transverse pivot axis. Each of the handle levers has a forward pivot pin and a rear pivot pin extending parallel to the transverse pivot axis. The transverse pivot axis and the forward and rear pivot pins are normal to the plane of the handle levers. The tool has first and second opposed die cutting jaws connected to the handle levers by engagement of the forward and rear pivot pins for movement toward and away from each other. Each jaw is connected to the forward pivot pin of one handle lever and to the rear pivot pin of the opposite handle lever in corresponding pivot pin receiving openings in each jaw. At least one of the pivot pin receiving openings in each jaw is longitudinally elongated.
The Hartmeister tool also has a pair of guide pins extending between the die cutting jaws and slidable with respect to at least one of the jaws. The pins are spaced apart, each near a forward or rear pivot pin and lying in the plane of the handle levers. The guide pins are approximately in longitudinal alignment with the cutting edges of the jaws.
The guide pins provide for accurate and consistent operation of the jaws as cutting dies. However, when the guide pins need to be replaced for any reason, the tool must be disassembled and the pins forcibly removed from the jaw in which they are rigidly mounted. Further, the use of two guide pins in the plane of the handles requires considerable precision and accuracy in attaching one of the jaw handles to the other.
The Hartmeister tool also has a spring between the die cutting jaws for biasing the jaws apart. The spring is located between the guide pins.
The present invention is a parallel action die cutting hand tool generally of the type described in U.S. Pat. No. 4,272,888 to Hartmeister. In one embodiment of the invention, the guide pins lie outside of and parallel to the plane of the handle levers. The guide pins may be located on the same side of the plane of the handle levers, or on opposite sides of the plane. In each of the first two embodiments, the pins are mounted in guide members removably attached to the cutting jaws.
A third embodiment of the invention has guide pins lying in the plane of the handle levers, and located on opposite sides of the cutting edges. A fourth embodiment of the invention has a single guide pin only. The single guide pin lies in the plane of the handle levers and is located approximately midway between the forward pivot pins and the transverse pivot axis.